Electrotherapy apparatus with superimposed AC fields

ABSTRACT

An electrotherapeutic field stimulator includes at least a pair of electrodes for applying the electricity to the body in the form of an electric field and a generator for providing the electricity to the electrodes in the form of at least two superimposed alternating current fields of different frequencies to provide the treatment waveform.

BACKGROUND OF THE INVENTION

The invention relates to an electrotherapy apparatus of the type whichexposes muscle tissue to an electrical current.

Electrotherapy apparatus are used in many ways for the treatment ofmuscles and nerves. Use is made of the circumstance that tissue, as arule, is not electrically neutral but carries electrical charges in theform of ions. To influence tissue in a non-mechanical manner, electricalor magnetic fields must act on the ions and these fields produce forces.The nature of the forces occurring is determined substantially by theshape, the amplitude and the timing of the applied fields. If a tissueis exposed to a DC electrical field, ions constantly flow down on theone side of this tissue and up again on the other side. Since chemicalcompounds can be broken down by the removal of ions, the tissue changesits structure under the protracted action of direct current. If,however, a rapid change in the polarity of the applied field occurs,whether on the basis of a sinusoidal alternating current, or on thebasis of positive or negative voltage pulses, no lasting changes of thetissue occur at certain frequencies, because the ions do not move veryfar from their original position. They then oscillate to some extentaround this original position and cause, among other things, a warmingof the tissue.

In order to achieve specific therapeutic effects it is already known toexpose muscles or nerves to electrical and/or magnetic fields of givenfrequency and amplitude (J. Low and A. Reed: Electrotherapy Explained,Butterworth-Heinemann Ltd., 1990, pp. 28 to 42, ISBN 0-07 506 00497). Adistinction is made between voltages which have a length or duration ofmore than 1 millisecond and currents having a length of less than 1millisecond. Also, currents or voltages are distinguished which changegradually or abruptly. The gradually varying electrical factors aresubdivided into sinusoidal, diadynamic, "Russian," interfering andhigh-frequency factors.

For the treatment of muscular crippling a stimulating current apparatusis known which is applied to a patient's skin by means of an electrode(DE-A-29 08 365). This stimulating current apparatus first emits aunipolar series of pulses of a first polarity for a certain time, andthen reverses the polarity and emits a unipolar series of pulses of asecond polarity. The direct-current average of the two series of pulsesis zero. Pauses of given lengths can be inserted between the pulseseries. The series of pulses are intended for the purpose of greatlyreducing the skin irritation which can be caused by the formation ofacid between the skin and the electrodes.

Also known is an apparatus for electrostimulation with which the milkglands of cows and other mammals are treated in order to increase milkoutput and the fat content of the milk, and to accelerate the milkingprocess (DE-C-29 29 293). This apparatus has a frequency modulator and apolarity setting means whereby pulses of a certain shape can begenerated. In particular, square wave pulses of given length andpolarity can be produced.

To stimulate and control smooth muscles and blood vessel tissues aprogrammable electrical apparatus is known by which succeeding positiveand negative pulses or pulse groups can be produced (EP-C-0 137007=AT-E-47 796). The pulses in this case rise with a time constant ofabout 40 milliseconds and fall again with the same time constant, thepulse width amounting to about 3 ms. The adjustable amplitudes of thepulses are between +130 V and -130 V, while the periods are preferably625 ms.

In another known apparatus for the electrostimulation of nerves andmuscles pulses are produced whose shape and frequency are adapted to thecharacteristics of the so-called slow muscle fibers (EP-C-0 197889=AT-E-52 927). The frequency and the duration of the pulse series canbe regulated.

In addition to direct current, pulsed current and simple alternatingcurrents, modulated alternating currents are also used forelectrotherapy. One of the modulated alternating currents is especiallythe so-called interference current, which is also called beat current orNemec current (Otto Steuernagel, Skripten zur Elektrotherapie, 3rd ed.,1976, Vol. II, p. 6, published by the author). A distinction is madebetween endogenic and exogenic interference currents. In endogenicinterference currents two medium frequencies are produced outside of thehuman body, and then heterodyned inside the body. On the other hand, theexogenic interference currents are produced outside of the body and fedas already heterodyned currents to electrodes which are laid on thepatient.

The basic idea of beat current therapy is to use two heterodyned fieldsdeep within the body to achieve a stimulating effect and at the sametime keep the current density on the skin low. The heterodyning of twofrequencies not too far apart brings it about that, depending on thephasing, these two currents amplify at a certain point in time and atanother point in time they cancel one another (H. Jantsch and F.Schuhfried: Niederfrequente Strome zur Diagnostik und Therapie, 1974, p.147).

Furthermore, a heterodyne current therapy is known in which threealternating currents in the medium-frequency range of about 4 kHz aresuperimposed, which differ in frequency from one another only by a smallamount, so that beats result from the superimposition (DE-A-30 10 716).The current curves resulting from the superimposition have the shape ofsinusoidal envelope curves on both sides of the potential null line,while sine half-waves of large amplitude alternate with smallamplitudes, comparable to a two-sideband amplitude modulation withsuppressed carrier (cf. Meinke-Gundlach: Taschenbuch derHochfrequentztechnik, 4th Edition, Vol. 3, Systems, 1986, O 3, FIG. 3,illustration in the time part). In the center the half-waves of the beatenvelopes opposite one another at any time cancel their potential, i.e.,there are no direct-current components. Nevertheless the two electrodeswhich are brought against a muscle to be treated are still at potential,so that an alternating current symmetrical with the null line is stillflowing. The muscle is thus treated locally always in the same manner;any change in the preferred direction of treatment during a given timedoes not occur. A frequent result is muscular cramping, which isdisagreeable to the patient.

SUMMARY OF THE INVENTION

According to the invention, a first alternating current field with afundamental frequency of 0.1 to 5 Hz is imposed by the electrodes, and asecond field with a frequency of 1 to 100 Hz is imposed on the firstalternating field.

By the gradual change of polarity according to the fundamentalfrequency, the muscle is stimulated with direct current first from oneside and then from the other side, although the pulsating frequency beatstimulation is sustained. If the fundamental frequency is alow-frequency sinusoidal curve, the transition from one polarity to theother is very gentle, and the patient perceives it as pleasant.

Thus the advantages of direct-current treatment is combined by theinvention with the advantages of heterodyne treatment. Particularly whenthe amplitude of the heterodyne beat envelopes amounts to about half ofthe amplitude of the fundamental frequency, therapeutic successes areachieved. In this case the heterodyne beat envelopes wander to a certainextent just above the null line into the positive, and then they changeinto the negative etc. The disadvantages of direct-current treatment,which sometimes consist in a pronounced galvanization or faradization atthe electrodes, are avoided by the gradual change in the polarity of thefundamental oscillation. Thus injuries to the skin at the points incontact with the electrodes are prevented.

With the invention, therefore, the therapeutic nerve stimulation anddeep action of direct-current signals are achieved with an alternatingfield, which is pleasant and pain-free, that is, does not produce theknown irritation and painful reactions resulting from direct-currentpulses. On account of the great irritation produced by the applicationand removal of the electrodes it has not been possible heretofore toachieve with movable electrodes a stimulating action equivalent to thatof the direct-current signals. Also, with the invention a harmonicinteraction between agonist and antagonist is achieved, i.e., betweenactive and passive muscle groups which participate in a body movement.Also, the musculature of the spinal column can for the first time beactivated symmetrically, which permits a natural regulation of blockedvertebrae joints.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows an arrangement with two electrodes, a DC voltage source, amodulation voltage source and several switches,

FIG. 2 a graphic representation of a direct current on which a beatvoltage is superimposed,

FIG. 3 a representation like FIG. 2, in which there is a constant switchfrom positive to negative polarity and vice versa,

FIG. 4 a low-frequency AC curve on which a heterodyne is superimposed,

FIG. 5 a block diagram of a system for the production of the currentcurve of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 two hand electrodes 1 and 2 are shown, which are brought fromtwo sides, for example, against a muscle so that this muscle will belocated between the two electrodes 1 and 2. The hand electrodes aresupplied with a voltage U which is composed of a direct-current voltageU_(G) and a modulation voltage U_(M). The modulation voltage ispreferably a heterodyne which is formed by the superimposition of twoalternating voltages with a small frequency difference.

The DC voltage U_(G) is supplied by a DC source 3 to which a modulationvoltage source 4 is connected in series. The sum voltage U passesthrough closed switches 5 and 6 to the electrodes 1 and 2. Thus apositive potential is at the electrode 1 because this electrode 1 isconnected to the positive pole of the voltage source 3. Negativepotential, however, is at the electrode 2 because this electrode 2 isconnected through the modulation voltage source 4 to the negative poleof the voltage source 3.

By means of the switches 5, 6 and 7, 8, the polarity at the electrodes1, 2 can be reversed. If switches 5 to 8 assume those positions whichare represented in solid lines, a positive potential is on the electrode1 and a negative potential on electrode 2. If switches 5 to 8 assume thepositions indicated in broken lines, positive potential is on electrode2 and negative potential on electrode 1.

In FIG. 2, the two potentials at the electrodes 1 and 2 are represented,the upper half of FIG. 2 showing the potential at electrode 1 and thelower half the potential at electrode 2. The two potentials aresymmetrical with the null line. If one of the two electrodes is set atzero potential, which can be accomplished by grounding electrode 2,there is no change in the relative potentials of the two electrodes 1and 2. Just as before, electrode 1 is more positive than electrode 2.Instead of U_(G) /2, U_(G) is then present at the ungrounded electrode;i.e., the potential then consists of U-OV=U, and a corresponding directcurrent flows with an alternating current from electrode 1 superimposedon it to electrode 2, if the positive counting direction is selected.The muscle is subjected unilaterally to the direct-current portionflowing continuously in the same direction. This unilateral applicationcannot be reduced by the heterodyne current symmetrically applied to themuscle. By opening switches 5 and 6 and closing additional switches 7and 8 the polarity of the voltage can be reversed, so that thedirect-current component now flows in the reverse direction. The newpositions of switches 5 to 8 are represented by the switches 5' to 8' inbroken lines.

The potential represented in the lower part of FIG. 2 now is present atelectrode 1, while the potential represented in the upper part is on theelectrode 2.

It is noted that the switches represented in FIG. 1 can be in the formof thyristors, GTO thyristors or controlled transistors.

FIG. 3 shows how the voltage U varies when switches 5 to 8 are reversedat certain intervals of time. During a period T/2 the positive potentialU_(G) with the modulating potential U_(M) is on the one electrode 1,while the other electrode 2 is at ground potential, for example, whilein the next time period T/2 up to moment T the above-mentioned positivepotential is on the electrode 2 and electrode 1 is at ground potential.This polarity reversal is repeated every second, for example, so that analternating frequency of 0.5 Hz results which we shall call thefundamental frequency f_(g). A heterodyne frequency amounting to 10 Hz,for example, and designated f_(s) is superimposed on the alternatingvoltage with the fundamental frequency f_(g). The modulation frequencypertaining to it amounts to 5 Hz and is designated f_(m). The beatenvelopes have a height of U_(s) and correspond to twice the amount ofthe heterodyne amplitude U_(SO). The descending and rising flanks 10 and11 are likewise modulated with a heterodyne signal, although this is notshown in FIG. 3. On account of the abrupt voltage changes asuperimposition of harmonics also occur which make a preciserepresentation virtually impossible anyway. FIG. 2 is thus aquasi-idealized representation in which it is assumed that absolutelysteep flanks 10 and 11 are possible, although this is not the case inreality. FIG. 2 also does not show the true proportions among thefrequencies, but only their association with one another in principle.

The beat frequency is produced in the present case by thesuperimposition of an alternating voltage of 3990 Hz on an alternatingvoltage of 4000 Hz. For fs the following will apply:

    f.sub.s =f.sub.1 -f.sub.2 =4000 Hz-3990 Hz=10 Hz.

The amplitude of the fundamental frequency, i.e. U_(G), in a preferredembodiment of the invention is approximately twice as high as theamplitude U₅ of the heterodyne envelopes. This assures that theheterodyne envelopes are raised by the sine curve into the positiverange and then are lowered again into the negative range.

The fundamental frequency f_(g) is represented in FIG. 3 as a squarewave. This square wave can be transformed by a Fourier analysis intovarious sine and cosine waves. These waves include a sine wave with thefrequency f_(g) (see for example B. E. Philippow: TaschenbuchElektrotechnik, Vol. 1, Allgemeine Grundlagen, 3rd edition, 1986, p.269). Instead of a square wave a triangle wave or any other wave can beused. It is important only that this wave have a low fundamentalfrequency. If a sine wave with fundamental frequency is used as thebasis, the result will be the voltage curve in FIG. 4.

In this FIG. 4, the heterodyne envelope 13 modulates the fundamentalwave 12 with the frequency f_(s) =1/T, and the heterodyne envelope ischaracterized by the beat frequency f_(s) and the carrier frequencyf_(t). The carrier frequency f_(t) amounts, as already mentioned, toabout 4000 Hz. With a voltage U according to FIG. 4 at the electrodes 1and 2, i.e., with a heterodyned low-frequency sine wave, surprisingtherapeutic effects can be achieved. On the one hand the muscle beingtreated is subjected to a frequency of about 4000 Hz, which has theleast effect on the pain receptors of the skin. A frequency between,say, 3000 Hz and 4000 Hz is therefore perceived as pleasant by thepatient. On the other hand the delivery of the frequency between 3000 Hzand 4000 Hz is performed by means of the frequency envelopes of aheterodyne. This heterodyne, which consists in a continuous increasefollowed by a decrease of the amplitude of the carrier frequency f_(t)has a positive influence on the tissues, as it is known from what isknown as heterodyne therapy.

It is essential, however, that the voltage of the heterodyne curve beapplied once to one side of the muscle and once to the other side of themuscle. This effect is achieved by the relatively slow change in thepolarity of the fundamental frequency f_(g) . With the slow polarityalternation virtually the same effects are achieved as in direct-currenttherapy, but without having to put up with its disadvantages. Moreover,the advantages of alternating current therapy are fully retained.

In FIG. 5 is a block diagram of a system for the production of a voltagecurve according to FIG. 4.

In it can be seen two sine wave generators 20 and 21, of which the onegenerator 20 produces a voltage of 4000 Hz, while the other generatorprovides a voltage with a frequency of 3990. Through the conductors 28and 32, respectively, the two voltages are fed to a mixer circuit 22where the heterodyning takes place, so that a heterodyne voltageresults. The term mixer circuit is to be understood to mean a system forthe general, e.g., additive or multiplicative combining or superpositionof curves, not a frequency converter such as what is provided, say, in asuperheterodyne receiver between an RF input stage and an intermediatefrequency amplifier. This heterodyne voltage is fed through a conductor29 to a heterodyne amplifier 23 which amplifies the heterodyne voltageand feeds it to a modulator 24. The amplified heterodyne signal, whichpasses through a line 30 to the modulator 24, is modulated with asinusoidal voltage of about 0.1 to 1 Hz coming from a sinusoidal signalgenerator 27. From here the modulated signal passes through a line 31 toan output amplifier 25 which can be regulated by a resistance 26. Thetwo electrodes 1 and 2 are connected to the output of the outputamplifier 25 by the lines 34 and 35. The amplitude of the oscillator 21can be controlled by a resistance 36. In this manner it can be broughtabout that the amplitudes of the voltages of the two oscillators willalways be equal, which is especially important to the beat effect. Theamplifier 23 is therefore arranged between the two mixer stages 22 and24 so as to be able to adjust the ratio between the amplitude of thefundamental and the amplitude of the heterodyne band. As alreadymentioned, an amplitude ratio of 2:1 is especially advantageous.

Instead of a single heterodyne a heterodyne can also be superimposed onthe sinusoidal fundamental curve 12, which corresponds to a two-sidebandamplitude modulation with suppressed carrier.

The arrangement represented in FIG. 5 is only one of several possibleembodiments. The superimposition of the two precisely harmonic voltagesof the oscillators 20 and 21 corresponds to an amplitude modulated wavewith a single modulation frequency. It is therefore basically possibleto use the numerous modulators known in the field of amplitudemodulation for the production of the heterodynes since theamplitude-modulated waves are equivalent to the superposition of twoprecisely harmonic partial waves.

It is also to be noted that the analog curves represented in FIGS. 2 to4 can be digitalized by using the scanning theorem. To produce a curveas in FIG. 4, this curve can be scanned at at least twice the frequencyof the highest frequency occurring in this curve, and the resultantamplitude samples can be resolved into individual bits. These bits canbe fed into a read-only memory which then to some extent stores thecurve shape of FIG. 4. By means of appropriate pulse generators thiscurve shape can be retrieved repeatedly from the memory.

It is also to be noted that, instead of the external production of thecurve shape of FIG. 4, internal production is also possible. In thiscase different waves are fed to the muscle from the outside, which thenresult in the curve shape of FIG. 4 on the muscle itself.

It is particularly to be stressed that the therapeutic effect isespecially apparent if the ratio of the amplitude of the envelope of theheterodyne and the amplitude of the carrier sine wave is a minimum of1:1 and a maximum of 1:2. It is also important that the heterodyne curvebe produced by the superimposition of two voltages within the spectrumbetween 1 and 5,000 Hz.

I claim:
 1. Electrotherapy apparatus for treating tissue, said apparatuscomprisingelectrodes between which tissue can be disposed for treatment,means for producing a first alternating field between said electrodes,said first alternating field having a frequency between 0.1 Hz and 5 Hz;and means for superimposing a second alternating field with a frequencyof 1 to 100 Hz on said first field.
 2. Electrotherapy apparatus as inclaim 1 further comprising means for superimposing a third alternatingfield on said second field so that said second field serves as anenvelope of said third field, said third field having a higher frequencythan said second field.
 3. Electrotherapy apparatus as in claim 2wherein said third alternating field has a frequency between 3000 and4000 Hz.
 4. Electrotherapy apparatus as in claim 2 wherein said meansfor superimposing a second field comprises means for superimposingvoltages having two adjacent frequencies to produce a heterodyne curvewhich serves as said envelope.
 5. Electrotherapy apparatus as in claim 4wherein said adjacent frequencies have a difference of 10 Hz, wherebysaid second field has a frequency of 10 Hz.
 6. Electrotherapy apparatusas in claim 5 wherein said adjacent frequencies are 4000 Hz and 3990 Hz.7. Electrotherapy apparatus as in claim 4 wherein said means forsuperimposing a second field comprisesa first oscillator which outputs avoltage having one of said adjacent frequencies, a second oscillatorwhich outputs a voltage having the other of said adjacent frequencies,and a first mixer which superposes the output voltages of respectivesaid first and second oscillators.
 8. Electrotherapy apparatus as inclaim 7 further comprising a second mixer which superimposes said secondfield on said first field.
 9. Electrotherapy apparatus as in claim 8further comprising an amplifier between said first mixer and said secondmixer.
 10. Electrotherapy apparatus as in claim 8 further comprising anadjustable amplifier between said second mixer and said electrodes. 11.Electrotherapy apparatus as in claim 4 wherein said superimposedvoltages have the same amplitude.
 12. Electrotherapy apparatus as inclaim 4 wherein said first alternating field has an amplitude which isapproximately twice the height of said envelope.
 13. Electrotherapyapparatus as in claim 1 wherein said first alternating field is a squarewave alternating field.
 14. Electrotherapy apparatus as in claim 1wherein said first alternating field is a sinusoidal alternating field.15. Electrotherapy apparatus for treating tissue, said apparatuscomprisingelectrodes between which tissue can be disposed for treatment,means for producing an electric field having a carrier frequency f_(t)between said electrodes, said electric field having an amplitude, meansfor modulating said amplitude according to a modulation frequency f_(m)of 1 to 100 Hz, and means for reversing the polarity of said electrodesaccording to a fundamental frequency f_(g) of 0.1 to 5 Hz. 16.Electrotherapy apparatus as in claim 15 wherein said carrier frequencyf_(t) is 3000 to 4000 Hz.
 17. Electrotherapy apparatus as in claim 15wherein said fundamental frequency f_(g) is 0.1 to 1 Hz. 18.Electrotherapy apparatus as in claim 1 wherein said means for producingsaid electric field is an AC power supply having a voltage U_(M) andsaid means for reversing the polarity of said electrodes is an AC powersupply having a voltage U_(G), said apparatus comprising means forsuperimposing said voltage U_(G) on said voltage U_(M).